Three-dimensional non-woven media

ABSTRACT

A non-woven melt-blown filament medium includes a mass of essentially continuous melt-blown polymer filaments and an essentially continuous traversing melt-blown polymer filament extending through the mass. The mass has a depth dimension, a longitudinal dimension, and a latitudinal dimension. The mass includes a plurality of layers, each of the plurality of layers being generally oriented in the longitudinal and latitudinal dimensions. The traversing filament is generally oriented in the depth dimension and extends through at least one layer of the mass. In one embodiment, the mass is cylindrical in shape and the layers comprise concentric zones. The traversing filament is intentionally deposited and positioned to improve the physical properties of the mass.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/343,827, filed Oct. 23, 2001, for“Three-Dimensional Non-Woven Media,” by Thomas M. Aune, Clinton V. Kopp,Michael J. Madsen, Philip M. Rolchigo, and Travis G. Stifter. Referenceis made to U.S. patent application Ser. No. 09/296,070, now U.S. Pat.No. 6,358,417, filed on Apr. 21, 1999, for “Non-Woven Depth FilterElement”, U.S. Provisional Patent Application Ser. No. 10/278,322, filedOct. 23, 2002, for “Three-Dimensional Non-Woven Filter”, and U.S. patentapplication Ser. No. 10/279,043, filed Oct. 23, 2002, for “Process ForMaking Three-Dimensional Non-Woven Media”.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of melt-blownmedia, more specifically media that has reduced density whilemaintaining structural strength. Such media can provide beneficialapplication in many uses where desirable material properties include lowdensity and high void volume while maintaining a relatively rigidstructure, especially under pressure. Uses for such media includefiltration media for various applications such as particle filtration,coalescing of oils and leukocyte filtration. Other uses envisionedinclude insulation, impact absorbing protective and conformablematerial, and wicking media for evaporators.

Numerous apparatuses and processes for forming melt blown mediacomprised of a plurality of substantially continuous filaments currentlyexist in the prior art. In this art, fiber forming devices or fiberizerssuch as those described in U.S. Pat. No. 3,825,379 issued to Lohkamp etal. and U.S. Pat. No. 3,825,380 issued to Harding et al. are used tospray filaments of synthetic resinous material toward a collectiondevice. During this process, jets of air or other gases act on thefilaments to attenuate such filaments to a comparatively fine diameterand convey the same to the collection device. Fibers continue to buildup on the collection device until a mass of fibers of the desired sizeand morphology is achieved.

Several specific processes have evolved from this general concept. Oneof these processes is described in U.S. Pat. No. 3,849,241 issued toBuntin et al. It discloses a process die or fiberizer consisting of adie head containing separate passages for the filament material and theattenuating air. During operation, molten resinous material is forcedthrough one or more small holes or nozzles in the die head toward acollection device and is attenuated by air streams positioned on thesides of the material outlet holes. The collection method utilized withthis process includes a rotating drum to form a continuous mat. Anotherof these processes is described in U.S. Pat. No. 4,021,281, issued toPall. It describes the continuous formation of a melt blown media webonto a rotating drum, being deposited in the form of a tubular web thatcan be slit into flat media. Another process is exemplified by U.S. Pat.No. 4,240,864 issued to Lin et al. This patent discloses a process dieor nozzle block which delivers a plurality of filaments toward arotating collection device. Associated with the filaments areattenuating air streams which function to attenuate the filaments asthey travel toward the collection device. Lin et al. also disclose apress roll for varying the pressure applied to the accumulating fiberson the rotating mandrel so as to provide a filter of varying fiberdensity. Like the processes of Buntin et al. and Pall, the diameter ofthe individual filaments in the Lin et al. process is constantthroughout the entirety of the media. However, contrary to Buntin et al.and Pall, in the Lin et al. process, the resultant media arecontinuously urged off the rotating mandrel via the noncylindrical pressroll to produce a coreless depth filter element.

Another specific process is represented by U.S. Pat. Nos. 4,594,202 and4,726,901, both issued to Pall et al. Similar to the processes describedabove, the Pall process includes a fiberizer or fiberizer die having aplurality of individual nozzles through which the molten filament resinis forced toward a collection mandrel. Also similar to the otherprocesses described above, this process discloses the use of air or gasstreams for the purpose of attenuating the filaments as they traveltoward the collection mandrel. This process differs from the processesdescribed above, however, in that it discloses a means for varying thefiber diameter throughout the radial dimension of the filter element,while maintaining a substantially constant voids volume for each levelof fiber diameter variance. Pall et al. accomplish this by sequentiallyaltering certain parameters which affect the fiber diameter duringcollection of the filaments on the rotating mandrel.

Although each of the above specific processes is generally acceptablefor certain applications, each also has certain limitations. Forexample, one limitation of the Pall et al. (U.S. Pat. Nos. 4,594,202 and4,726,901) process is that it is a non-continuous or semi-continuousprocess. In other words, a filter element of finite length is formed bybuilding up a mat of attenuated filaments on a rotating mandrel. Whenthe collected filament material reaches a desired thickness, the filterstructure is removed and the process is commenced again for the nextfilter element.

Although the Pall et al. patents (U.S. Pat. Nos. 4,594,202 and4,726,901) contemplate a depth filter element comprised of filamentswith varying diameters, there are several limitations which exist.First, the process of Pall et al. is not a continuous process, but mustbe repeated for each filter manufactured. Second, although some filterelements of Pall et al. have filaments of varying diameters, the processof making such elements has limitations. Specifically, the filamentdiameter is varied by sequentially changing one of several operatingconditions of the filament producing mechanism. Whenever such a changeis introduced, however, the system takes time to respond to such changesbefore again reaching equilibrium. The time frame for response isproportional to the degree of change. Because these changes areintroduced during the manufacture of each individual filter element, aless stable and more variable process results. Further, the changeoverfrom a filament of one diameter to that of another occurs gradually as atime related transition, rather than abruptly such as where thestructure is comprised of two or more discrete filaments.

An important attribute of the media structure is the percent void volumewhich is the ratio of the air volume in the structure to the total mediastructure volume. The percent voids volume in the melt-blown mediashould be as high as possible in order to achieve a number of desirablecharacteristics in filtration applications, such as high dirt holdingcapacity and lower initial pressure drop. Generally, achieving a highvoid volume results in lowering the density of the media mass. It isalso desirable to lower the density of a media mass, because a lowerdensity media requires less material usage, allowing for lower materialcosts, higher throughput, and faster production.

Another advantage of media with high void volume is that they areamenable to insertion of a significant percentage volume of activeparticles or fibers without inducing an unacceptable increase inpressure drop in filtration applications. For example, activated carbonparticles may be dispersed in the media as they are formed. Moreover,masses with high void volumes and lower densities also generally provideadvantages for other applications such as thermal insulation,evaporative wicking and impact absorption material.

However, in prior art melt blown media, there is an upper limit beyondwhich further increasing the percent voids volume becomes undesirable.Attempts to produce low density, high void volume, media structuresusing the prior art teachings result in reduced fiber-to-fiber bondingand typically insufficient structural strength. As the voids volume isincreased in prior art structures, the fibrous media used in a depthfilter are more readily compressed by the pressure drop generated by thefluid passing through it. This is particularly troublesome when thefluid is viscous. If the percent void volume is too high, the filtermedium will begin to collapse at too low a differential pressure. As itcollapses, the pores become smaller and the differential pressureincreases, causing still more compression. The resulting rapid increasein pressure drop thus reduces the media's useful life and dirt holdingcapacity rather than—as might otherwise be expected with the increasedvoid volume media—extending it. Use of a very low density (high voidsvolume) can also make the filter very soft and thereby more readilydamaged in normal handling and more likely to compress and collapse inuse.

A drawback of the prior art products is that the low density filtersoften are made using fine fibers and therefore have a fine micronrating, which is inherent to the finer fiber matrix. It would bedesirable to use fine fibers to achieve low density, while maintainingthe capacity to produce media with a larger pore structure. For afiltration application, this would mean a coarser micron rating, therebyallowing for filtration of a wider range of particles without prematureclogging of the filter. This would require that the fine fiber networkis somehow fixed in a more open structure, thereby avoiding the naturalpacking tendency of the fine fibers that inherently create a finer porestructure.

Although prior art methods exist for manufacturing melt blown media,each of the methods, as well as the products constructed from suchmethods, have limitations of compressive strength at low mediadensities. Accordingly, there is a need in the art for an improved, costefficient melt blown media. A need also exists for a continuous methodand apparatus for producing such media.

BRIEF SUMMARY OF THE INVENTION

A non-woven melt-blown filament medium includes a mass of essentiallycontinuous melt-blown polymer filaments and an essentially continuoustraversing melt-blown polymer filament extending through the mass. Themass has a depth dimension, a longitudinal dimension, and a latitudinaldimension. The mass includes a plurality of layers, each of theplurality of layers being generally oriented in the longitudinal andlatitudinal dimensions. The traversing filament is generally oriented inthe depth dimension and extends through one or more layers of the mass.In one embodiment, the mass is cylindrical in shape and the layerscomprise concentric zones. In one embodiment, a core zone of the masshas filaments having a diameter; an intermediate zone of the mass hasfilaments having larger diameters than the filaments of the core zone;and an outer zone of the mass has filaments having larger diameters thanthe filaments of the intermediate zone. In one embodiment, thetraversing fiber is a bonding fiber bonding one or more layers of themass together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram generally illustrating a system forcontinuously producing a non-woven depth filter element.

FIG. 2 is a schematic diagram illustrating the system configuration forcontinuously producing a depth filter element of the present invention.

FIG. 2A is an enlarged view of the collection device of the apparatus ofFIG. 2.

FIG. 3 illustrates an elevation view of a depth filter element of thepresent invention viewed from line 3—3 of FIG. 2A.

FIG. 4 is a schematic diagram generally illustrating a second embodimentof the system for continuously producing a non-woven depth filterelement.

FIG. 5 is a schematic diagram illustrating the system configuration forthe embodiment of FIG. 4.

FIG. 6 illustrates an elevation view of a second embodiment of a depthfilter element of the present invention viewed from line 6—6 of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention of melt blown media with improved structuralstrength can be used in various formats for melt blown media includingcontinuously formed cartridge filters, continuously formed webs,structural composite webs, and pre-impregnated fiber reinforcing mats.The melt blown media of the present invention comprise a mass ofessentially continuous polymer filaments. The media have a length orlongitudinal dimension, a width or latitudinal dimension, and a depthdimension. The primary filaments of the melt blown media are generallyoriented in the length (x or longitudinal) and width (y or latitudinalor circumferential in the case of a cylindrical mass) dimensions. Animportant feature of the invention is that the media also compriseessentially continuous polymer filaments extending in the depth (z)dimension. The concurrent formation of primary fibers in the x and ydimensions and separate bonding fibers in the z dimension allows fordesign and engineering of specific zones of media for specificapplication needs. The invention also includes a method of continuouslyproducing the melt blown media.

One important embodiment of the melt blown media comprises a cylindricalmass of essentially continuous polymer filaments. The cylindrical masshas a longitudinal or x dimension, a circumferential or y dimension anda radial or z dimension. The primary filaments of the cylindrical massare generally oriented in the longitudinal and circumferential or x andy dimensions. The filament mass also comprises essentially continuouspolymer filaments extending throughout the cylindrical mass in theradial or z dimension. These melt blown media are particularly usefulfor producing a filament mass to use in constructing a depth filterelement. In a tubular filter, for example, the media of the presentinvention allow for the formation of a self supporting interior corezone that concurrently provides a zone of critical filtration. Byplacing a higher percentage of the bonding filaments in the core zoneand those zones next to the core, the filter can be engineered to haveboth higher crush strengths and lower density than if the same amount ofbonding filaments were evenly distributed throughout the media. Theinvention also includes a method of continuously producing the filamentmass.

One useful demonstrated application for the invention is for particlefiltration and more particularly for use in a depth filter cartridgecomprising a filter element constructed of a plurality of substantiallycontinuous filaments which are collected to form a generally tubulardepth filter cartridge. The present invention also relates to a methodand system for making such a filter cartridge.

To obtain the unique, combined benefit of a low density and rigidlyfixed media structure requires implementation of two or moreconcurrently formed melt blown media. A very fine matrix of primaryfibers with reduced fiber to fiber bonding is used to form a structurewith low density. A second source of filaments is concurrently andintentionally placed in the z dimension onto the primary media as theyare forming to provide improved fiber to fiber bonding as well asinterlocking the mechanical structure. These z filaments thereby form amore rigid porous structure which has significantly greater mechanicalstrength. The primary media are typically formed in essentiallytwo-dimensional layers with the fibers oriented in the x and y axes andwith only incidental bonding between layers. It has been discovered thatit is beneficial to place the bonding z filaments in the forming layersof primary media fibers and across two or more of the formed primarymedia layers, with these bonding z filaments essentially oriented in thez-axis with respect to the primary media. This permits concurrent,continuous production of very fine melt-blown media that are relativelyrigid and wherein the fibers are structurally locked in place.

It has also been found beneficial to insert the bonding z filamentsacross the primary media as they are forming, so the bonding z filamentsextend across one or more zones of the primary media. It has also beenfound beneficial for the bonding z filaments to extend across all thelayers of the primary media, and thereby to traverse from one majorsurface of the finished primary media to the other major surface. In adescribed embodiment of this invention, the z filament is used as abonding filament to produce low density primary media that have improvedresistance to compression. It is envisioned that the insertion of thebonding z filament across one or more layers of the primary media asthey are forming could be used to produce media with other significantbenefits. For example, the z polymer could have significantly differentphysical or chemical characteristics which could result in a significantimprovement in the composite media produced. The ability to engineer theplacement, composition and physical attributes of these z filaments isvery useful and offers the opportunities to explore media structures notpossible in the current art.

Another aspect of the present invention is the application of a thinlayer of bonding fibers at one or both surfaces of the forming media toprovide a more finished porous surface. The bonding fibers adhere to theprimary media fibers at the surface and thereby eliminate loose fibersat the media surface. Another significant benefit discovered is that thebonding fibers adhere to the primary surface fibers and conform to thetexture of the surface. The bonding fibers then shrink as they cool,which intensifies the resulting surface roughness. The resultingfinished surface was surprisingly found to have about twice the surfacearea of an unfinished primary media surface. This increased surface areaprovides a number of benefits, especially useful for particle filtrationapplications. Doubling the surface area of the shell can allow the shellto have a lower porosity while not causing an excessive pressure drop.Also, as the filter is used, a cake of particles can collect on theshell surface and also cause increased pressure drop. The high surfacearea permits extended operation before such pressure drop increases areincurred. Also, in a cartridge filter embodiment, the formation of arelatively hard shell avoids the necessity to encapsulate the filter ina support cage after the filter cartridge is produced.

A preferred embodiment of the present invention is an improved non-wovenfilament mass for use in constructing a depth filter element as well asa system and a method for continuously making such a mass. However, itshould be understood that other embodiments are also contemplated. Forexample, while a cylindrical product is described in the preferredembodiment, the teachings of the invention may be adapted for flat,sheet, or planar products. Such a flat product may be produced, forexample, by manufacturing the medium on a large drum and then cuttingthe resulting cylindrical medium along its length to obtain a sheet ofmaterial.

FIG. 1 generally illustrates one embodiment of a system which is used tocontinuously manufacture filament mass of indefinite length. The masscan then be cut into a plurality of individual filament elements ofdesired length. A similar system is disclosed in U.S. Pat. No. 5,340,479by Szczepanski, et al., which is fully incorporated herein by reference.The illustrated embodiment of system 10 includes motor driven screw typeextruder 12 which is supplied with thermoplastic polymeric material froma source (not shown). The particular thermoplastic polymeric materialmay be any one of a variety of synthetic resinous materials which canproduce the filaments used in manufacturing the depth filter element ofthe present invention. Although the class of polymeric materials knownas polypropylenes is preferred, polyesters, Nylon, polyurethanes andother materials may be used as well.

Within extruder 12, the polymeric material is heated to a molten state,at which time it is metered and conveyed into heated delivery line 14.The material is maintained or further heated in line 14 and isultimately directed to a filament forming means, which in one embodimentis in the form of two filament delivery systems 16 and 18. Each of thedelivery systems 16 and 18 produces one or more substantially continuouspolymeric filaments and directs the same along a predetermined pathtoward a collection means as will be described in greater detail below.

Filament delivery system 16 includes a motor driven gear type positivedisplacement metering pump 20 which receives molten polymeric materialfrom heated delivery line 14 and pumps it to heater block 22. The speedof motor 24 which drives metering pump 20, and thus the rate at whichthe material is metered through pump 20 is electronically controlled byan appropriate controller 26.

Heater block 22, which is independently heated via heating means (notshown) is provided with internal passages which lead to a plurality ofnozzles 27, 28, and 29. The heating means, and thus the temperature ofthe polymeric material within heater block 22, is controlled bytemperature control 30. Each nozzle 27, 28, and 29 includes an orifice,the size of which may be selected as desired to assist in achieving adesired filament size or diameter. The molten material fed to eachnozzle 27, 28, and 29 exits the respective orifice in a stream.

Associated with each nozzle 27, 28, and 29 are attenuating mechanisms31, 32, and 33, which comprise a plurality of gas or air jets. Gasflowing out of the attenuating mechanisms 31, 32, and 33 function toattenuate the stream of molten material exiting from nozzles 27, 28, and29 to form polymeric filaments in a manner known in the art. Attenuatingmechanisms 31, 32, and 33 accordingly may be of any design known in theart including that described in U.S. Pat. No. 4,173,443 by Lin, thedisclosure of which is incorporated herein by reference.

Attenuating mechanism 31 is associated with an optional gas heater 34and gas supply source 36. Gas supply source 36 provides gas via conduit38 and appropriate valves and regulators to heater 34. The temperatureof heater 34 is elevated or lowered to the desired temperature viatemperature control 40. The gas is then fed from heater 34 throughconduit 42 to attenuating mechanism 31. Attenuating mechanisms 31, 32,and 33 may be provided with gas from a common supply source such asdescribed with reference to FIG. 1 or alternatively, separatelycontrolled gas sources may be employed for each attenuating mechanism31, 32, and 33.

Filament delivery system 18 is substantially similar to that of system16 described above, except that filament delivery system 18 preferablyincludes a means of delivering the filaments in such a manner as toactively intermingle with filaments produced by one or more of thenozzles used in system 16. Filament delivery system 18 may include oneor more polymer extrusion nozzles. One embodiment uses one nozzle 44which includes a sweep mechanism for attenuator 54 (shown later withrespect to FIG. 2). Specifically, system 18 includes heater block 46,independently driven positive displacement metering pump 48 and motor50. Heater block 46 is provided with nozzle 44 and temperature control52. System 18 is also provided with attenuating mechanism 54 associatedwith nozzle 44. Pressurized gas is passed to attenuating mechanism 54from gas supply source 56 via conduit 58. As with delivery system 16,each of the attenuators in system 18 can be associated with optional gasheaters, not shown. The provision of separate filament delivery systems16 and 18 enables separate control and production of polymeric filamentsproduced by each system 16 and 18.

Delivery systems 16 and 18 produce streams of discrete, essentiallycontinuous polymer filaments which are distributed in flared patterns66, 68, 70, and 72 and directed from nozzles 27, 28, 29, and 44 andattenuating mechanisms 31, 32, 33, and 54, respectively, toward filamentcollection device 74. There is preferably some overlap in adjacentfilament patterns 66, 68, and 70 so that the filaments of each patternconnect with the filaments of the respective adjacent patterns,resulting in an integrated tubular filament mass. Filament collectiondevice 74 includes central, rotatable collection device 76 such as amandrel or drum, which extends from drive motor 78. Press roll member80, which rotates about axle shaft 81, is disposed adjacent to mandrel76 and spaced therefrom.

During operation, the essentially continuous polymer filaments ofstreams 66, 68, and 70 are directed in a flared pattern toward rotatingmandrel 76 and collected thereon in a manner known in the art. Whilemandrel 76 is shown, it is contemplated that other collection devicesmay also be used, such as large diameter drums. Simultaneously,reciprocating or oscillating stream 72 deposits an essentiallycontinuous filament or fiber stream which spans the distance between afar edge 82 of stream 66 and a far edge 84 of stream 70 and traversesthe layers of filaments laid down by streams 66, 68, and 70. Rotatingpress roller 80 engages the filaments which have accumulated on rotatingmandrel 76. As sufficient filaments are built up on mandrel 76, pressroller 80 forces non-woven filament mass or fiber structure 86 off theaxial end of mandrel 76 in the direction of arrow 88 to produce acontinuous filament mass 86 of indefinite length. Filament mass 86 has aradial dimension, a longitudinal dimension, and a circumferentialdimension. The entire filament collection device 74 may be similar tothat described in U.S. Pat. No. 4,240,864 by Lin, the disclosure ofwhich is incorporated herein by reference.

For a more complete understanding of the present invention, reference ismade to FIG. 2, which is a schematic diagram illustrating the apparatusof FIG. 1 configured for continuously producing a depth filter elementof the present invention. As shown in FIG. 2, four filament producingdevices are employed, each of which comprises a nozzle and anattenuating mechanism, such as nozzles 27, 28, 29, and 44 andattenuating mechanisms 31, 32, 33, and 54. Nozzles 27, 28, and 29 arelongitudinally aligned along common axis 90, which is preferably about0–15 degrees offset from parallel to mandrel 76. In a preferredembodiment, nozzles 27, 28, and 29 are positioned about 4 inches apart.Each nozzle 27, 28, and 29 includes an orifice which defines an axis 92,94, and 96, respectively, that is preferably perpendicular to axis 90and about 0–15 degrees offset from perpendicular to mandrel 76. Axes 93,94, and 96 generally correspond to the flow axis of molten polymerexiting the respective nozzle orifice. In one preferred embodiment,nozzles 27, 28, and 29 are located approximately 35–40 inches frommandrel 76, which preferably spins at a rate of about 400 RPM. Thisorientation results in flared filament patterns 66, 68, and 70 beingdirected toward mandrel 76.

Filament patterns 66, 68, and 70 are comprised of polymer filamentshaving diameters of between less than about 1 micron to about 100microns. In a preferred embodiment, filament pattern 66 comprisesfilaments of the smallest diameter; filament pattern 68 comprisesfilaments of intermediate diameter; and filament pattern 70 comprisesfilaments of the largest diameter. As a non-limiting example, polymerfilaments of filament patterns 66, 68, and 70 were produced in a depthfilter by extruding polypropylene heated to a temperature of betweenabout 325° C. and about 400° C. through a nozzle having an orifice sizeof about 0.016 inch at a rate of about 11 pounds per hour and passing anambient gas at a temperature of about 25° C. at a rate of about 13standard cubic feet per minute over the molten polymer stream exitingthe nozzle orifice. It will be appreciated that a person skilled in theart can readily determine other suitable parameter combinations. It canbe appreciated that the operating parameters may be varied betweenfilament patterns 66, 68, and 70 to produce zones of varying densitiesand fiber sizes.

Opposite filament patterns 66, 68, and 70, nozzle 44 and attenuatingmechanism 54 produce filament pattern 72. As better seen in FIG. 2A,filament pattern 72 comprises pattern 72A which moves in areciprocating, transverse pattern, preferably covering the distancebetween the primary pattern edges 82 and 84. Alternatively, filamentpattern 72 covers less than the distance between edges 82 and 84.Filament pattern 72 preferably originates from one or more nozzles 44located in a position above or below press roll 80 so that pattern 72travels from nozzle 44 to mandrel 76 and lands on the forming filamentmass 86 without spraying directly onto press roll 80.

Attenuating mechanism 54 preferably includes servo driven sweepmechanism 98 (see FIG. 2) which allows attenuating mechanism 54 to sweepthrough an angle so that the filament pattern 72A (see FIG. 2A)traverses back and forth among fiber patterns 66, 68, and 70, along alongitudinal dimension of filament mass 86. As pattern 72A traversesfiber patterns 66, 68, and 70, it deposits essentially continuouspolymer filaments across the overall laydown pattern which extendsbetween the primary pattern edges 82 and 84. In formed filament mass 86,the fibers of filament pattern 66 deposited along edge 82 will form afirst major surface 97 (shown in FIG. 3), and the fibers of filamentpattern 70 deposited along edge 84 will form a second major surface 99(shown in FIG. 3). In another embodiment, nozzle 44 may be oscillatedback and forth to sweep bonding filament pattern 72.

In a preferred embodiment shown in FIG. 2, sweep mechanism 98 comprisesa servo drive motor with a cam and follower mechanism. Other suitabledevices, such as AC/DC driven mechanical cranks and push rod mechanisms,for example, are also acceptable. In a preferred embodiment, sweepmechanism 98 runs at about 950 oscillations per minute. As depicted,attenuating mechanism 54 of nozzle 44 is oriented to produce gas streamswhich result in flared filament pattern 72 being directed toward mandrel76.

In one preferred embodiment, nozzle 44 is located approximately 18–22inches from mandrel 76. Because nozzle 44 is positioned much closer tomandrel 76 than nozzles 27, 28, and 29, the fibers of filament pattern72 have less time to cool before contacting filament mass 86 and aretherefore hotter and more adhesive than fibers of filament patterns 66,68, and 70. Preferably, the fiber of filament pattern 72 is stillrelatively liquid when it contacts the fibers of filament patterns 66,68, and 70. Because a skin or shell has not completely formed on thefiber of filament pattern 72, it instantaneously adheres to the fibersof filament patterns 66, 68, and 70 upon contact. However, someattenuation or cooling of the fiber of filament pattern 72 is requiredto avoid melting of the fibers of filament patterns 66, 68, and 70.

In an alternative embodiment, rather than locating nozzle 44 closer tomandrel 76 than nozzles 27, 28, and 29, attenuating mechanism 54 may useless air or warmer air than attenuating mechanisms 31, 32, and 33. Thisarrangement will also result in fibers of filament pattern 72 beinghotter and more adhesive than fibers of filament patterns 66, 68, and70. Other process alternatives known in the art may be used to deliverfibers of filament pattern 72. For example, it is also envisioned thatfibers of pattern 72 could be colder than those of filament patters 66,68, and 70 so as to lend mechanical advantage rather than thermalbonding, as taught in an embodiment above.

Filament pattern 72 is comprised of polymer filaments having diametersof between less than about 1 micron to about 100 microns. As anon-limiting example, polymer filaments of filament pattern 72 areproduced in the depth filter of the instant invention by passingpolypropylene heated to a temperature of between about 325° C. and about400° C. through a nozzle having an orifice size of about 0.016 inch at arate of about 8 pounds per hour and passing at an ambient gas at atemperature of about 25° C. at a rate of about 7 standard cubic feet perminute over the molten polymer stream exiting the nozzle orifice. Itwill be appreciated that a person skilled in the art can readilydetermine other suitable parameter combinations.

As more completely shown in FIG. 2A, which is an enlarged view of thecollection device of FIG. 2, an accumulated mass of filaments 86 isproduced on mandrel 76. Filament pattern 72 comprises reciprocatingcone-shaped filament pattern 72A, which sweeps between pattern edges 82and 84 to produce an overall wider cone-shaped pattern 72. In oneembodiment, press roller 80 is oriented at an angle relative to mandrel76 with nip 100 in contact with mandrel 76. As a non-limiting example,outer surface 102 of press roller 80 is angularly displaced by about 3°relative to mandrel 76. In one embodiment, nip 100 contacts mandrel 76close to edge 82 of filament pattern 66. Because of the angularplacement of press roller 80, compression of filaments in collectivefilament mass 86 varies along the length of press roller 80. Thisresults in a filament mass having a varying density gradient in theradial dimension, with the filament density of filament pattern 66 beinggenerally greater than that of the filament mass comprised of filamentpatterns 68 and 70.

Fibers from filament patterns 66, 68, and 70 form a generallytwo-dimensional mat or layer of material that is continuously formed onmandrel 76 to build up filament mass 86 composed of many layers offibers. These fibers can be described as being laid down in an X-Yplane, or in the longitudinal and circumferential or latitudinaldimensions. As the fibers are built up, layer upon layer, they produce aradial or depth dimension. The sweeping motion of filament pattern 72A,combined with the rotation of mandrel 76 causes the fibers coming fromnozzle 44 to integrate into mass 86 as a “z” direction fiber, extendingradially through the zones produced by filament patterns 66, 68, and 70.

FIG. 3 illustrates an elevation view of filament mass 86 viewed fromline 3—3 of FIG. 2A. Filament mass 86 comprises first major surface 97,second major surface 99, and concentric filtration zones 104, 106, and108, with additional filament mass strength in the radial directionprovided by filament 110. Filament 110 serves as a fiber structurestrengthening element. Filament 110 extends throughout filament mass 86and extends in the radial, longitudinal, and circumferential dimensions.

Generally, filament zone 104 is produced by filament pattern 66;filament zone 106 is produced by filament pattern 68; filament zone 108is produced by filament pattern 70; and filament 110 is produced byfilament pattern 72. Filtration zones 104, 106, and 108 preferablypossess different physical characteristics. For example, filtration zone104 may comprise relatively smaller diameter filaments; filtration zone106 may comprise intermediate diameter filaments; and filtration zone108 may comprise larger diameter filaments. Filtration zones 104, 106,and 108 preferably have filaments having diameters ranging in size fromless than about 1 micron to about 100 microns. Filaments 110 and 172 mayhave diameters which are equal to, greater than, or less than an averagediameter of the filaments of filtration zones 104, 106 and 108. In someembodiments, filtration zone 104 may have a relatively high density offilaments; filtration zone 106 may have an intermediate density offilaments, and filtration zone 108 may have a lower density offilaments. In another embodiment, filtration zones 104, 106 and 108 mayhave other variations in density.

In one embodiment, there is generally an absence of fiber-to-fiberbonding within each of the masses 104, 106, and 108. The primary bondingwithin filament mass 86 is accomplished by the bonding between “z”direction fiber 110 and the filaments of zones 104, 106, and 108.Selected zones of the media can be made very rigid to provide afiltering layer which also carries the resultant mechanical loads,thereby eliminating the need for separate structural elements in a givenfilter device.

FIG. 3. illustrates, for one embodiment, approximately the orientationof “z” fiber 110, as it is laid down during one revolution of mandrel 76(shown in FIG. 2A). In this embodiment, the relation between the rate ofmovement of the servo driven sweep of “z” fiber 110 and the rate ofrotation of mandrel 76 are such that the “z” fibers 110 are placed in acontinuous manner from the core or bottom zone 104 to the shell or topzone 108 and back to the core zone 104 of mass 86 during approximately120 degrees or less of rotation during the forming of mass 86. The pathof “z” fiber 110 in one rotation of mandrel 76 can be described asfollows. When filament pattern 72A is near pattern edge 82, “z” fiber110 is laid onto filament mass 86 near the core of core zone 104. Asfilament pattern 72A sweeps toward pattern edge 84, “z” fiber 110 islaid across zones 104, 106, and 108 until it reaches the outside ofshell zone 108. Mandrel 76 spins while filament pattern 72A sweeps sothat “z” fiber 110 also travels in a circumferential direction aroundfilter mass 86. Thus, “z” fiber 110 runs radially, longitudinally, andcircumferentially throughout filter mass 86. In the case where mass 86is planar rather than cylindrical, “z” fiber 110 may be described asextending in the length, width, and thickness dimensions of mass 86.

Filter mass 86 is built up only after many revolutions of mandrel 76,and thus filter mass 86 includes a web of “z” fibers 110 which act tohold together fibers from zones 104, 106, and 108 in all threedimensions, thereby lending strength to filament mass 86 and providingtensile support. Because the fibers of mass 86 are held in place in allthree directions, bending moments of the fine fibers are minimized,thereby minimizing dirt release and channeling at increased pressuredrops. Such undesirable dirt release and channeling would otherwise beexpected when using such fine fibers in a low density media.

In one embodiment, the fibers of zones 104, 106, and 108 comprise about75–95 percent of the fibers of filter mass 86, and “z” fibers 110comprise about 5–25 percent of the fibers of filter mass 86; morepreferably, the fibers of zones 104, 106, and 108 comprise about 80–90percent of the fibers of filter mass 86, and “z” fibers 110 compriseabout 10–20 percent of the fibers of filter mass 86; most preferably,the fibers of zones 104, 106, and 108 comprise about 85 percent of thefibers of filter mass 86, and “z” fibers 110 comprise about 15 percentof the fibers of filter mass 86. In a preferred embodiment, sweepmechanism 98 is adjustable to control the amount of “z” fiber 110deposited in each zone 104, 106, and 108. In one embodiment, a higherpercentage of “z” fiber 110 is deposited in core zone 104 than in zones106 and 108. This may be accomplished by slowing the sweep of mechanism98 in core zone 104. For example, “z” fiber 110 may make up about 25% ofthe total fibers in core zone 104 and about 3% in shell zone 108. Thisconfiguration provides added strength to the core region of filter mass86, which is required to maintain the filter's crush resistance as it isused.

The fibers of zones 104, 106, and 108 may be comprised of differentmaterials, may be of different sizes, or may otherwise have differingproperties. For example, the diameters of the fibers in each zone mayget progressively larger from core zone 104 to shell zone 108. Each zonemay also possess a different density from each adjacent zone. Forexample, the density of the zones may decrease progressively from corezone 104 to shell zone 108. Other alternatives will be evident to oneskilled in the art.

The unique construction of filament mass 86 allows for a high voidvolume without sacrificing strength by fixing the fibers into an open,yet supported structure. Thus, the filament mass 86 of the presentinvention displays significantly greater mechanical strength to weightratios than media of the prior art. Filament mass 86 may be formed toany thickness desired. In one embodiment, filament mass 86 has an insidediameter of about 1.15 inch and an outside diameter of about 2.5 inches.In one embodiment, filament mass 86 has a mass of about 95 grams or lessper ten inch section and a crush strength of at least about 40 psi. Ahigh void volume results in a filament mass 86 with greater dirt holdingcapacity, longer element life, and lower pressure drop. Moreover, itallows filament mass 86 to be produced faster and with less material,compared with conventional filters. In a preferred embodiment, a teninch section of filament mass 86 can be produced in about 15 seconds andhas a retention rating of 90% at 20 microns.

FIG. 4 is a schematic diagram generally illustrating a second embodimentof the system for continuously producing a non-woven depth filterelement. FIG. 4 is similar to FIG. 1 but further includes filamentdelivery system 114, nozzle 116, attenuating mechanism 118, flarepattern 120, and shell-forming filament delivery system 122. Additionalnozzle 116, attenuating mechanism 118, and flare pattern 120 are similarto the nozzles 27, 28 and 29; attenuating mechanisms 31, 32, and 33; andflare patterns 66, 68 and 70 described above. While four such nozzles,attenuating mechanisms, and flare patterns are shown for filamentdelivery system 16, it is contemplated that more or fewer may be used.In one embodiment, nozzles 27, 28, 29 and 116 are positioned about 35inches to about 40 inches from mandrel 76.

Filament delivery system 114 is substantially similar to that of system16 described above, except that filament delivery system 114 preferablyincludes a means of delivering the filaments in such a manner that theyintermingle with filaments produced by one or more of the nozzles usedin system 16. Filament delivery system 114 may include one or morepolymer extrusion nozzles. One embodiment uses one nozzle 124 withattenuator 126, positioned at an acute angle relative to mandrel 76 todeliver a filament pattern or stream 128 which contacts filament mass127 in an elliptical pattern which intermingles with filament patterns66, 68, 70 and 120 and those of filament delivery system 18.

Specifically, system 114 includes heater block 130, independently drivenpositive displacement metering pump 132 and motor 134. Heater block 130is provided with nozzle 124 and temperature control 136. System 114 isalso provided with attenuating mechanism 126 associated with nozzle 124.Pressurized gas is passed to attenuating mechanism 126 from gas supplysource 138 via conduit 140. As with delivery system 16, attenuators 126can be associated with an optional gas heaters, not shown. The provisionof separate filament delivery systems 18 and 114 enables separatecontrol and production of polymeric filaments produced by each system 18and 114, although each of the filament delivery systems 18 and 114produces filaments which traverse filament mass 127 in a radial, or z,dimension. In one embodiment, the source of material for filamentdelivery system 114 is extruder 12 via delivery line 14; in anotherembodiment, the material source for system 114 is separate to providealternate materials to those used in filament delivery systems 16, 18and 122.

Delivery system 114 produces a stream of a discrete, essentiallycontinuous polymer filament which is distributed in flared pattern 128and directed from nozzle 124 and attenuating mechanism 126 towardfilament collection device 74. During operation, the filament of stream128 is directed in a flared pattern toward rotating mandrel 76. In oneembodiment, filament pattern 128 spans the distance between a far edge82 of stream 66 and a far edge 142 of stream 120. In an alternativeembodiment, filament pattern 128 does not span the distance between faredges 82 and 142, but does cover a significant portion of the forminglayers of filament mass 127, e.g., the distance covered by filamentpattern 128 is greater than the distance covered by each primaryfilament stream 66, 68, 70 and 120 individually. Preferably the distancecovered by filament pattern 128 is greater than the distance covered bytwo or more adjacent primary filament streams 66, 68, 70 and 120. In oneembodiment, nozzle 124 is placed about 10–13 inches from mandrel 76. Inone embodiment, nozzle 124 is placed at an acute angle of about 10° toabout 20° relative to mandrel 76, and more preferably about 15° relativeto mandrel 76.

Shell-forming filament delivery system 122 is substantially similar tosystem 16 described above, except that shell-forming filament deliverysystem 122 is preferably configured and positioned to produce arelatively smooth outer shell zone 112 (see FIG. 6) on the exteriorcylindrical surface of filament mass 127. Shell-forming filamentdelivery system 122 preferably uses a different location, polymerthroughput rate, and air attenuation setting relative to filamentdelivery system 16. Compared to system 16, nozzle 144 is preferablyplaced closer to mandrel 76 and uses a lower polymer throughput rate;additionally, attenuating mechanism 146 uses less air attenuation.Similar to system 16, shell-forming filament delivery system 122includes heater block 148, metering pump 150, motor 152, temperaturecontrol 154, gas supply source 156, and conduit 158.

As a non-limiting example, polymer filaments of filament pattern 162 wasproduced in a depth filter by extruding polypropylene heated to atemperature of between about 270° C. and about 325° C. through nozzle144 having an orifice size of about 0.016 inch at a rate of about 1pound per hour and passing an ambient gas at a temperature of about 25°C. at a rate of about 1.5 standard cubic feet per minute over the moltenpolymer stream exiting the nozzle orifice. In one embodiment, nozzle 144is placed about 3–6 inches from mandrel 76. It will be appreciated thata person skilled in the art can readily determine other suitableparameter combinations.

Nozzle 144 is preferably placed so that the filament produced thereby isdeposited on the outer zone 170 formed by filament pattern 120 (as shownin FIG. 6). This configuration produces a very shallow zone or shell 112with significant fiber-to-fiber bonding, including some bonding betweenthe fibers of shell 112 and the fibers of outer zone 170. Thefiber-to-fiber bonding of shell 112 essentially eliminates the presenceof loose fibers on the surface 99 of the finished filament mass 127 andsignificantly increases the surface area of the resulting surface 99.

FIG. 5 is a schematic diagram illustrating the system configuration forthe embodiment of FIG. 4. As shown in one embodiment in FIG. 5, filamentdelivery system 16 includes four filament producing devices, each ofwhich comprises a nozzle and an attenuating mechanism, such as nozzles27, 28, 29 and 116 and attenuating mechanisms 31, 32, 33 and 118.Nozzles 27, 28, 29 and 116 are longitudinally aligned along common axis90, which is preferably about 0–15 degrees offset from parallel tomandrel 76. In a preferred embodiment, nozzles 27, 28, 29 and 116 arepositioned about 4 inches apart. Each nozzle 27, 28, 29 and 116 includesan orifice which defines an axis 92, 94, 96 and 160, respectively, thatis preferably perpendicular to axis 90 and about 0–15 degrees offsetfrom perpendicular to mandrel 76. Axes 93, 94, 96 and 160 generallycorrespond to the flow axis of molten polymer exiting the respectivenozzle orifice. In one preferred embodiment, nozzles 27, 28, 29 and 116are located approximately 40 inches from mandrel 76, which preferablyspins at a rate of about 400 RPM. This orientation results in flaredfilament patterns 66, 68, 70 and 120 being directed toward mandrel 76.

Filament patterns 66, 68, 70 and 120 are comprised of polymer filamentshaving diameters of between less than about 1 micron to about 100microns. In a preferred embodiment, filament pattern 66 comprisesfilaments of the smallest diameter; filament pattern 68 comprisesfilaments of intermediate diameter; filament pattern 70 comprisesfilaments of larger diameter; and filament pattern 120 comprisesfilaments of the largest diameter. As a non-limiting example, polymerfilaments of filament patterns 66, 68, 70 and 120 were produced in adepth filter by extruding polypropylene heated to a temperature ofbetween about 325° C. and about 400° C. through a nozzle having anorifice size of about 0.016 inch at a rate of about 11 pounds per hourand passing an ambient gas at a temperature of about 25° C. at a rate ofabout 13 standard cubic feet per minute over the molten polymer streamexiting the nozzle orifice. It will be appreciated that a person skilledin the art can readily determine other suitable parameter combinations.It can be appreciated that the operating parameters may be variedbetween filament patterns 66, 68, 70 and 120 to produce zones of varyingdensities and fiber sizes.

Filament pattern 72 comprises pattern 72A which moves in areciprocating, transverse pattern, preferably covering the distancebetween the primary pattern edges 82 and 142. Alternatively, filamentpattern 72 covers less than the distance between edges 82 and 142.Attenuating mechanism 54 preferably includes servo driven sweepmechanism 98 which allows attenuating mechanism 54 to sweep through anangle so that the filament pattern 72 traverses back and forth amongfiber patterns 66, 68, 70 and 120, along a longitudinal dimension offilament mass 127. As pattern 72A traverses fiber patterns 66, 68, 70and 120, it deposits essentially continuous polymer filaments across theoverall laydown pattern which extends between the primary pattern edges82 and 142. In formed filament mass 127, the fibers of filament pattern66 deposited along edge 82 will form a first major surface 97 (shown inFIG. 6), and the fibers of filament pattern 70 deposited along edge 84will form a second major surface 99 (shown in FIG. 6). In anotherembodiment, nozzle 44 may be oscillated back and forth to sweep bondingfilament pattern 72.

Fibers from filament patterns 66, 68, 70 and 120 form a generallytwo-dimensional mat or layer of material that is continuously formed onmandrel 76 to build up filament mass 127 composed of many layers offibers. These fibers can be described as being laid down in an X-Yplane, or in the longitudinal and circumferential or latitudinaldimensions. As the fibers are built up, layer upon layer, they produce aradial or depth dimension. The sweeping motion of filament pattern 72A,combined with the rotation of mandrel 76 causes the fibers coming fromnozzle 44 to integrate into mass 127 as a “z” direction fiber, extendingradially through the zones produced by filament patterns 66, 68, 70 and120.

In the embodiment shown in FIG. 5, filament pattern 128 is preferablyproduced simultaneously by nozzle 124 and attenuating mechanism 126,located about 13 inches from mandrel 76. In one embodiment, nozzle 124and attenuating mechanism 126 are preferably static or stationary, inthat filament pattern 128 does not oscillate or reciprocate likefilament pattern 72A. In an alternative embodiment, pattern 128 isoscillated or reciprocated. The filament from pattern 128 preferablymixes with the filament from pattern 72 across filament patterns 66, 68,70 and 120. This is accomplished in one embodiment by introducingfilament pattern or stream 128 at an acute angle relative to mandrel 76,resulting in a highly elliptical cross section of filament pattern 128contacting the rotating, forming filament mass 127.

As shown in FIG. 5, sweeping filament stream 72A intercepts filamentstream 128, helping to secure the filaments of stream 128 to the formingfilament mass 127. Further, nozzle 144 and attenuating mechanism 146preferably direct shell-forming filament pattern 162 onto a portion offilament mass 127 which has substantially reached its finishedcircumference.

FIG. 6 illustrates an elevation view of a second embodiment of a depthfilter element of the present invention viewed from line 6—6 of FIG. 5.Filament mass 127 includes first major surface 97, second major surface99, and concentric filtration zones 164, 166, 168 and 170, withadditional filament mass strength in the radial direction provided byfilaments 110 and 172. Filaments 110 and 172 serve as a strengtheningelement for fiber structure 127. Filaments 110 and 172 extend throughoutfilament mass 127 and extend in the radial, longitudinal, andcircumferential dimensions.

Generally, filament zone 164 is produced by filament pattern 66;filament zone 166 is produced by filament pattern 68; filament zone 168is produced by filament pattern 70; filament zone 170 is produced byfilament pattern 120; filament 110 is produced by filament pattern 72;and filament 172 is produced by filament pattern 128. Filtration zones164, 166, 168 and 170 preferably possess different physicalcharacteristics. For example, filtration zone 164 may compriserelatively smaller diameter filaments; filtration zones 166 and 168 maycomprise intermediate diameter filaments; and filtration zone 170 maycomprise larger diameter filaments. Filtration zones 164, 166, 168 and170 preferably have filaments having diameters ranging in size from lessthan about 1 micron to about 100 microns. In another embodiment, forexample, filtration zone 164 may have a relatively high density offilaments; filtration zones 166 and 168 may have an intermediate densityof filaments, and filtration zone 170 may have a lower density offilaments.

In one embodiment, there is generally an absence of fiber-to-fiberbonding within each of the masses 164, 166, 168 and 170 produced byfilament patterns 66, 68, 60 and 120, respectively. The primary bondingwithin filament mass 127 is accomplished by the bonding between “z”direction fibers 110 and 172 and the filaments of zones 164, 166, 168and 170. Selected zones of the media can be made very rigid to provide afiltering layer which also carries the resultant mechanical loads,thereby eliminating the need for separate structural elements in a givenfilter device.

Fibers 110 are produced as described with reference to FIG. 3 above.Fibers 172 are formed as follows: when the filament stream of filamentpattern 128 is near pattern edge 82, “z” fiber 172 is laid onto filamentmass 127 near the area of surface 97. As the filament stream of filamentpattern 128 flares toward pattern edge 142, “z” fiber 172 is laid acrosszones 164, 166, 168 and 170 until it reaches the outside of outer zone170. Mandrel 76 spins while filament pattern 128 sprays so that “z”fiber 172 also travels in a circumferential direction around filter mass127. Thus, “z” fiber 172 runs radially, longitudinally, andcircumferentially throughout filter mass 127. In the case where mass 127is planar rather than cylindrical, gluing fiber 172 may be described asextending in the length, width, and thickness dimensions of mass 127.

In a preferred embodiment, filament pattern 128 is positioned so thatthe elliptical cross sectional area that contacts fiber mass 127transverses one or more zones 164, 166, 168 and 170; however, filamentpattern 128 need not transverse all zones 164, 166, 168 and 170. Theelliptical cross section of filament pattern 128 results in alongitudinal component of orientation. The forming fiber mass 127 uponwhich filament stream 128 is laid has a conical shape resulting in aradial component of orientation. Mandrel 26 spins, providing filament172 with a circumferential component of orientation around filter mass127. Thus, “z” fiber 172 runs radially, longitudinally andcircumferentially throughout filter mass 127. While one nozzle 124 isshown to produce filaments 172, it is contemplated that a differentnumber of nozzles with other positions and configurations may also beused.

In one embodiment, the fibers of zones 164, 166, 168 and 170 compriseabout 75–95 percent of the fibers of filter mass 127, and “z” fibers 110and 172 comprise about 5–25 percent of the fibers of filter mass 127;more preferably, the fibers of zones 164, 166, 168 and 170 compriseabout 80–90 percent of the fibers of filter mass 127, and “z” fibers 110and 172 comprise about 10–20 percent of the fibers of filter mass 127;most preferably, the fibers of zones 164, 166, 168 and 170 compriseabout 85 percent of the fibers of filter mass 127, and “z” fibers 110and 172 comprise about 15 percent of the fibers of filter mass 127.

A new and unexpected property of the media of the present invention isthat a strong integral filtration core may be produced withoutsignificantly increasing the density of the media. This is accomplishedby depositing bonding fibers 110 and 172 onto the primary filtrationfibers of zones 164, 166, 168 and 170 during the melt blowing process.The additional heat energy of bonding fibers 110 and 172 allow thehighly amorphous polypropylene primary filtration fibers tosignificantly increase in crystallinity, which, in turn, strengthens themedia.

The fibers of zones 164, 166, 168 and 170 may be comprised of differentmaterials, may be of different sizes, or may otherwise have differingproperties. For example, the diameters of the fibers in each zone mayget progressively larger from core zone 164 to outer zone 170. Each zonemay also possess a different density from each adjacent zone. Forexample, the density of the zones may decrease progressively from corezone 164 to outer zone 170. Moreover, in one embodiment, one or both of“z” fibers 110 and 172 have different material properties than theprimary fibers of zones 162, 166, 168 and 170. For example, fibers 110and/or 172 may be catalysts for reactions or absorbent or adsorbentmaterials for toxins, viruses, proteins, organics, or heavy metals. In apreferred embodiment, the diameters of structural strengthening fibersor filaments 110 and 172 are comparable to the diameters of the primaryfiltration fibers in zones 164, 166, 168 and 170 so that the fibers 110and 172 contribute not only to the strength of filament mass 127, butalso to its filtration capabilities. Other alternatives will be evidentto one skilled in the art.

Depth filter elements formed in the manner described herein havedemonstrated excellent particle filtration and fluid throughputcapabilities. For example, the depth filter of the present invention hasbeen demonstrated to have about twice the life and dirt holding capacitycompared to similarly rated filters (e.g., 90% effective at removing 20micron particles). Furthermore, the depth filter element of the presentinvention allows fluid throughput with a minimal drop in fluid pressureacross the filter.

Filter performance depends on a combination of a number of factors,including the following: the size of contaminants that the filter canremove (efficiency), the amount of contaminants the filter can holdbefore plugging (dirt holding capacity), and the reliability of thefilter function throughout its life or under variable operatingconditions.

For any given filter, the dirt holding capacity (DHC) and filterefficiency are generally inversely related. The mass of a particlevaries with the cube of its radius; therefore, lower efficiency filtersthat trap only larger particles and let the smaller particles pass cangain more weight before plugging.

To one skilled in the art, it is evident that DHC and filter cartridgeweight are also generally inversely related. Reducing the weight of afixed-volume filter cartridge is accomplished by taking material out ofthe cartridge, which in turn leaves more space (void volume) in whichthe trapped contaminants may accumulate. It is also apparent that takingmaterial out of the cartridge, with all other variables held constant,makes the cartridge weaker (lower filter crush strength).

Filter crush strength is a typical measurement used to gauge thedurability of a filter cartridge. If a filter is too soft, it will notfunction reliably throughout its service life or under variableoperating conditions. To one skilled in the art of melt blowing, it isapparent that filter crush strength at a fixed filter weight can bemanipulated by changing the fiber diameter as well as other processparameters; generally, larger fibers produce higher crush strength.Changing the filter construction to larger fibers generally increasesthe pore size to some degree, resulting in lower retention efficiency.

In order to take these major filter performance and constructionvariables into consideration for the purpose of filter comparison, theMadsen performance ratio (M) has been developed.M _(ratio)=(DHC×crush strength)/(μm@90%×filter weight)

-   -   DHC is in grams    -   crush strength is in pounds per square inch (psi)    -   μm@90% refers to the particle size (μm) at which the filter        produces 90% efficiency    -   filter weight (unused filter) is in grams

Higher ratio values indicate better utilization of the material in thefilter, meaning that the filter has a better balance of strength, dirtholding capacity, and removal efficiency than filter with lower ratiovalues.

Although the description of the preferred embodiments and methods havebeen quite specific, it is contemplated that various modifications couldbe made without deviating from the spirit of the present invention.Accordingly, it is intended that the scope of the present invention bedictated by the appended claims rather than by the description of theillustrated embodiments. For example, it is contemplated that theteachings of the present invention may be adapted for flat or sheet typefilters and products of other configurations. Additionally, theinvention may also be practiced using “z” fibers 172 without “z” fibers110, or vice versa. One advantage of the use of both “z” filamentdelivery systems 18 and 114 is that a system of multiple sources offersan operator a greater degree of control. Additionally, while onefilament delivery system of each type 16, 18, 114 and 122 is shown, itis contemplated that multiple systems of one or more types may also beused.

Moreover, it is contemplated that the roles of the filaments from thevarious delivery systems may be interchanged. For example, in oneembodiment, the primary filtration filaments are produced by system 16and bonding or structural strengthening filaments are produced bysystems 18 and 114. In another embodiment, the primary filtrationfilaments are produced by one or both of systems 18 and 114, and bondingor structural strengthening filaments are produced by system 16. Theoperating parameters and conditions can be manipulated by one ofordinary skill to obtain the desired combination of filaments in a mass.

EXAMPLE 1

Comparing a filter of the present invention with a standard filter, thefollowing results were found for filters for a 10 micron particle size(A.C. fine test dust):

crush strength weight of 10″ life dirt holding product (psi) cartridge(g) (minutes) capacity (g) invention 93 133 60 60 standard 125  205 2933 control 42 143

In all three examples, the standard product is made by any of the priorart methods discussed in the background of the invention. The controlproduct is made by the same method as the invention, but without the zfilaments 110 and 172. This is accomplished by turning off the materialpumps to nozzles 44 and 124. Additionally, the control filter cartridgewas allowed more time to form in order to compensate for the decreasedinput of material and allow it to reach a comparable weight compared tothe invention product using z filaments 110 and 172. Other operatingconditions for formation of the “invention” and the “control”cylindrical cartridges are described below.

In this example, the filter of the present invention was much lighterthan the standard filter, lasted about twice as long, and had abouttwice the DHC of the standard filter. However, it had a lower crushstrength. Applying the formula above, M_(ratio-invention)=4.2 andM_(ratio-standard)=2.0. Thus, the filter of the present inventionperforms better than the standard product. The control product wastested only for crush strength. At a weight comparable to the inventionproduct, the control product exhibited less than half the crush strengthof the invention product.

In this example, the filter of the present invention was produced usingprimary fiber filament patterns 66, 68, 70 and 120 created by extrudingpolypropylene heated to between about 360° C. and about 400° C. throughnozzles 27, 28, 29 and 116 having an orifice size of about 0.016 inch ata rate of about 9.5 pounds per hour. Filament streams 66 and 68 wereheated to about 400° C., and filament streams 70 and 120 were heated toabout 360° C. Attenuating mechanisms 31, 32, 33 and 118 passed ambientgas at a temperature of about 25° C. and had flow rates between about10.5 to about 15 cubic feet per minute over the molten polymer streamsexiting from nozzles 27, 28, 29 and 116. The flow rate of attenuatingmechanism 31 was at about 15 cubic feet per minute over nozzle 27 andthe flow rates of attenuating mechanisms 32, 33 and 118 progressivelydecreased to a flow rate of about 10.5 cubic feet per minute atattenuating mechanism 118 over nozzle 116. Nozzles 27, 28, 29 and 116were positioned at a distance of between about 35 and about 37 inchesfrom mandrel 76.

“Z” fiber filament pattern 128 was produced by extruding polypropyleneheated to about 370° C. through nozzle 124 having an orifice size ofabout 0.016 inch at a rate of about 5.5 pounds per hour. Attenuatingmechanism 126 passed ambient gas at a temperature of about 25° C. andhad a flow rate of about 9 cubic feet per minute over the polymer streamexiting nozzle 124. Nozzle 124 was positioned at a distance about 13inches from mandrel 76.

“Z” fiber filament pattern 72A was produced by extruding polypropyleneheated to about 370° C. through nozzle 44 having an orifice size ofabout 0.016 inch at a rate of about 5.5 pounds per hour. Attenuatingmechanism 54 passed ambient gas at a temperature of about 250° C. andhad a flow rate of about 7 cubic feet per minute over the polymer streamexiting nozzle 44. Nozzle 44 was positioned at a distance about 21inches from mandrel 76.

Shell forming fiber filament pattern 162 was produced by extrudingpolypropylene heated to about 280° C. through nozzle 144 having anorifice size of about 0.016 inch at a rate of about 1.0 pound per hour.Attenuating mechanism 146 passed ambient gas at a temperature of about25° C. and had a flow rate of about 1.25 cubic feet per minute over thepolymer stream exiting nozzle 144. Nozzle 144 was positioned at adistance about 3.5 inches from mandrel 76.

EXAMPLE 2

Comparing a filter of the present invention with a standard filter, thefollowing results were found for filters for a 20 micron particle size(A.C. coarse test dust):

crush strength weight of 10″ life dirt holding product (psi) cartridge(g) (minutes) capacity (g) invention 83 119 85 118 standard 100  160 46 65 control 36 129

In this example, the filter of the present invention was lighter thanthe standard filter, lasted about twice as long, and had almost twicethe DHC of the standard filter. However, it had a lower crush strength.Applying the formula above, M_(ratio-invention) =4.1 andM_(ratio-standard)=2.0. Thus, the filter of the present inventionperforms better than the standard product. The control product wastested only for crush strength. At a weight comparable to the inventionproduct, the control product exhibited less than half the crush strengthof the invention product.

In this example, the filter of the present invention was produced usingprimary fiber filament patterns 66, 68, 70 and 120 created by extrudingpolypropylene heated to about 370° C. through nozzles 27, 28, 29 and 116having an orifice size of about 0.016 inch at a rate of between about 10to about 11 pounds per hour. Nozzles 27 and 28 had a flow rate of about10 pounds per hour and nozzles 29 and 116 had greater flow rates ofapproximately 11 pounds per hour. Attenuating mechanisms 31, 32, 33 and118 passed ambient gas at a temperature of about 25° C. and had flowrates between about 10.5 to about 15 cubic feet per minute over themolten polymer streams exiting from nozzles 27, 28, 29 and 116. The flowrate of attenuating mechanism 31 was at about 15 cubic feet per minuteover nozzle 27 and the flow rates of attenuating mechanisms 32, 33 and118 progressively decreased to a flow rate of about 10.5 cubic feet perminute at attenuating mechanism 118 over nozzle 116. Nozzles 27, 28, 29and 116 were positioned at a distance of between about 38 and about 40inches from mandrel 76.

“Z” fiber filament pattern 128 was produced by extruding polypropyleneheated to about 370° C. through nozzle 124 having an orifice size ofabout 0.016 inch at a rate of about 6 pounds per hour. Attenuatingmechanism 126 passed ambient gas at a temperature of about 25° C. andhad a flow rate of about 12 cubic feet per minute over polymer streamexiting nozzle 124. Nozzle 124 was positioned at a distance about 13inches from mandrel 76.

“Z” fiber filament pattern 72A was produced by extruding polypropyleneheated to about 370° C. through nozzle 44 having an orifice size ofabout 0.016 inch at a rate of about 6 pounds per hour. Attenuatingmechanism 54 passed ambient gas at a temperature of about 25° C. and hada flow rate of about 11 cubic feet per minute over the polymer streamexiting nozzle 44. Nozzle 44 was positioned at a distance about 22inches from mandrel 76.

Shell forming fiber filament pattern 162 was produced by extrudingpolypropylene heated to about 290° C. through nozzle 144 having anorifice size of about 0.016 inch at a rate of about 1.1 pound per hour.Attenuating mechanism 146 passed ambient gas at a temperature of about25° C. and had a flow rate of about 1.75 cubic feet per minute over thepolymer stream exiting nozzle 144. Nozzle 144 was positioned at adistance about 3.5 inches from mandrel 76.

EXAMPLE 3

Comparing a filter of the present invention with a standard filter, thefollowing results were found for filters for a 30 micron particle size(A.C. coarse test dust):

crush strength weight of 10″ life dirt holding product (psi) cartridge(g) (minutes) capacity (g) invention 75 113 105 120 standard 80 152  50 73 control 43 106

In this example, the filter of the present invention was lighter thanthe standard filter, lasted about twice as long, had a much greater DHC,and had a comparable crush strength. Applying the formula above,M_(ratio-invention)=2.7 and M_(ratio-standard) =1.3. Thus, the filter ofthe present invention performs better than the standard product. Thecontrol product was tested only for crush strength. At a weightcomparable to the invention product, the control product exhibitedsignificantly lower crush strength compared to the invention product.

In this example, the filter of the present invention was produced usingprimary fiber filament patterns 66, 68, 70 and 120 created by extrudingpolypropylene heated to about 360° C. through nozzles 27, 28, 29 and 116having an orifice size of about 0.016 inch at a rate of between about 10to about 11 pounds per hour. Nozzles 27 and 28 had a flow rate of about10 pounds per hour and nozzles 29 and 116 had greater flow rates ofabout 11 pounds per hour. Attenuating mechanisms 31, 32, 33 and 118passed ambient gas at a temperature of about 25° C. and had flow ratesbetween about 10.5 to about 15 cubic feet per minute over the moltenpolymer streams exiting from nozzles 27, 28, 29 and 116. The flow rateof attenuating mechanism 31 was at about 15 cubic feet per minute overnozzle 27 and the flow rates of attenuating mechanisms 32, 33 and 118progressively decreased to a flow rate of about 10.5 cubic feet perminute at attenuating mechanism 118 over nozzle 116. Nozzles 27, 28, 29and 116 were positioned at a distance of between about 38 and about 40inches from mandrel 76.

“Z” fiber filament pattern 128 was produced by extruding polypropyleneheated to about 360° C. through nozzle 124 having an orifice size ofabout 0.016 inch at a rate of about 6 pounds per hour. Attenuatingmechanism 126 passed ambient gas at a temperature of about 25° C. andhad a flow rate of about 12 cubic feet per minute over the polymerstream exiting nozzle 124. Nozzle 124 was positioned at a distance about13 inches from mandrel 76.

“Z” fiber filament pattern 72A was produced by extruding polypropyleneheated to about 360° C. through nozzle 44 having an orifice size ofabout 0.016 inch at a rate of about 6 pounds per hour. Attenuatingmechanism 54 passed ambient gas at a temperature of about 25° C. and hada flow rate of about 11 cubic feet per minute over the polymer streamexiting nozzle 44. Nozzle 44 was positioned at a distance about 22inches from mandrel 76.

Shell forming fiber filament pattern 162 was produced by extrudingpolypropylene heated to about 280° C. through nozzle 144 having anorifice size of about 0.016 inch at a rate of about 1.1 pound per hour.Attenuating mechanism 146 passed ambient gas at a temperature of about25° C. and had a flow rate of about 1.75 cubic feet per minute over thepolymer stream exiting nozzle 144. Nozzle 144 was positioned at adistance about 3.5 inches from mandrel 76.

1. A non-woven melt-blown filament medium, the filament mediumcomprising: a mass of melt-blown polymer filaments, the mass having adepth dimension, a longitudinal dimension, and a latitudinal dimension;the filaments of the mass being generally oriented in the longitudinaland latitudinal dimensions, the mass comprising a plurality of zones inthe depth dimension having different characteristics; and a traversingmelt-blown polymer filament generally oriented to extend through thelongitudinal, latitudinal and depth dimensions of the mass, so that thetraversing filament extends in the depth dimension through two or morezones.
 2. The filament medium of claim 1 in which the filaments of themass have an average diameter, and in which the traversing filament hasa diameter about equal to the average diameter of the filaments of themass.
 3. The filament medium of claim 1 in which the filaments of themass have an average diameter, and in which the traversing filament hasa diameter greater than the average diameter of the filaments of themass.
 4. The filament medium of claim 1 in which the filaments of themass have an average diameter, and in which the traversing filament hasa diameter less than the average diameter of the filaments of the mass.5. The filament medium of claim 1 in which each zone comprisingcomprises filaments of different size than each adjacent zone.
 6. Thefilament medium of claim 1 in which a ratio of an amount of traversingfilament to an amount of all the filaments of a zone is different ineach zone compared to each adjacent zone.
 7. The filament medium ofclaim 1 in which each zone has a different density than each adjacentzone.
 8. The filament medium of claim 5 in which the mass comprises: afirst zone of polymer filaments; a second zone adjacent the first zone,the second zone comprising polymer filaments generally having largerdiameters than the filaments of the first zone; and a third zoneadjacent the second zone, the third zone comprising polymer filamentsgenerally having larger diameters than the filaments of the second zone.9. The filament medium of claim 8 in which a ratio of an amount oftraversing filament to an amount of all the filaments of a zone ishigher in the first zone than in the third zone.
 10. The filament mediumof claim 1 in which the mass is cylindrical and comprises a plurality ofconcentric zones, each zone having a different density than eachadjacent zone.
 11. The filament medium of claim 10 in which thecylindrical mass comprises: a core zone of polymer filaments; anintermediate zone of polymer filaments surrounding the core zone, theintermediate zone being generally less dense than the core zone; and anouter zone of polymer filaments surrounding the intermediate zone, theouter zone being generally less dense than the intermediate zone. 12.The filament medium of claim 1 wherein the polymer filaments of thelayers of the mass exhibit minimal filament to filament bonding.
 13. Thefilament medium of claim 1 in which the traversing filament bondstogether the filaments of the mass through which it extends.
 14. Thefilament medium of claim 1 in which the traversing filament structurallyinterlocks the filaments of the mass through which it extends.
 15. Thefilament medium of claim 1 in which the traversing filament crystallizesthe filaments of the mass through which it extends.
 16. The filamentmedium of claim 1 in which the traversing filament is made of adifferent polymer than the filaments of the mass.
 17. The filamentmedium of claim 16 in which the traversing filament comprises anadsorbent material.
 18. The filament medium of claim 16 in which thetraversing filament comprises an absorbent material.
 19. The filamentmedium of claim 16 in which the traversing filament comprises acatalyst.
 20. A non-woven melt-blown filament medium, the filamentmedium comprising: a mass of essentially continuous melt-blown polymerfilaments, the mass having a depth dimension, a longitudinal dimension,and a latitudinal dimension; the filaments of the mass comprising aplurality of layers, each of the plurality of layers being generallyoriented in the longitudinal and latitudinal dimensions, the masscompring a plurality of zones in the depth dimension having differentcharacteristics; and an essentially continuous traversing melt-blownpolymer filament generally oriented to extend in the longitudinal,latitudinal and depth dimensions of the mass and extending in the depthdimension through the plurality of zones.
 21. The filament medium ofclaim 20 in which the filaments of the mass have an average diameter,and in which the traversing filament has a diameter about equal to theaverage diameter of the filaments of the mass.
 22. The filament mediumof claim 20 in which the filaments of the mass have an average diameter,and in which the traversing filament has a diameter greater than theaverage diameter of the filaments of the mass.
 23. The filament mediumof claim 20 in which the filaments of the mass have an average diameter,and in which the traversing filament has a diameter less than theaverage diameter of the filaments of the mass.
 24. The filament mediumof claim 20 in which each zone comprises filaments of different sizethan each adjacent zone.
 25. The filament medium of claim 20 in which aratio of an amount of traversing filament to an amount of all thefilaments of a zone is different in each zone compared to each adjacentzone.
 26. The filament medium of claim 20 in which each zone has adifferent density than each adjacent zone.
 27. The filament medium ofclaim 24 in which the mass comprises: a first zone of essentiallycontinuous polymer filaments; a second zone adjacent the first zone, thesecond zone comprising essentially continuous polymer filamentsgenerally having larger diameters than the filaments of the first zone;and a third zone adjacent the second zone, the third zone comprisingessentially continuous polymer filaments generally having largerdiameters than the filaments of the second zone.
 28. The filament mediumof claim 27 in which a ratio of an amount of traversing filament to anamount of all the filaments of a zone is higher in the first zone thanin the third zone.
 29. The filament medium of claim 20 in which the massis cylindrical and comprises a plurality of concentric zones, each zonehaving a different density than each adjacent zone.
 30. The filamentmedium of claim 29 in which the cylindrical mass comprises: a core zoneof essentially continuous polymer filaments; an intermediate zone ofessentially continuous polymer filaments surrounding the core zone, theintermediate zone being generally less dense than the core zone; and anouter zone of essentially continuous polymer filaments surrounding theintermediate zone, the outer zone being generally less dense than theintermediate zone.
 31. The filament medium of claim 20 wherein theessentially continuous polymer filaments of the layers of the massexhibit minimal filament to filament bonding.
 32. The filament medium ofclaim 20 in which the traversing filament bonds together the layersthrough which it extends.
 33. The filament medium of claim 20 in whichthe traversing filament structurally interlocks the layers through whichit extends.
 34. The filament medium of claim 20 in which the traversingfilament crystallizes the filaments of the layers through which itextends.
 35. The filament medium of claim 20 in which the traversingfilament is made of a different polymer than the filaments of the mass.36. The filament medium of claim 35 in which the traversing filamentcomprises an adsorbent material.
 37. The filament medium of claim 35 inwhich the traversing filament comprises an absorbent material.
 38. Thefilament medium of claim 35 in which the traversing filament comprises acatalyst.
 39. A three-dimensional non-woven melt-blown polymeric fiberstructure having first and second major surfaces, the structurecomprising: a plurality of layers of essentially continuous melt-blownpolymer fibers forming a plurality of zones in a depth dimension havingdifferent characteristics between the first and second major surfaces;and a melt-blown fiber structural strengthening element that traverses aplurality of the layers between the first and second major surfaces andengages fibers of the layers, the melt-blown fiber structuralstrengthening element being generally oriented to extend throughlongitudinal, latitudinal and depth dimensions of the plurality oflayers so that it extends in the depth dimension from the first majorsurface to the second major surface through the plurality of zones. 40.The fiber structure of claim 39 n which the fibers of the plurality oflayers have an average diameter, and in which the fiber structuralstrengthening element has a diameter about equal to the average diameterof the fibers of the plurality of layers.
 41. The fiber structure ofclaim 39 in which the fibers of the plurality of layers have an averagediameter, and in which the fiber structural strengthening element has adiameter greater than the average diameter of the fibers of theplurality of layers.
 42. The fiber structure of claim 39 in which thefibers of the plurality of layers have an average diameter, and in whichthe fiber structural strengthening element has a diameter less than theaverage diameter of the fibers of the plurality of layers.
 43. The fiberstructure of claim 39 further comprising a density gradient across theplurality of layers.
 44. The fiber structure of claim 43 in which theplurality of zones comprise: a lower zone of layers adjacent the firstmajor surface; and an upper zone of layers adjacent the second majorsurface, the upper zone comprising essentially continuous polymer fibersgenerally having larger diameters than the fibers of the lower zoned.45. The fiber structure of claim 44 further comprising: an intermediatezone between the lower zone and the upper zone, the intermediate zonecomprising essentially continuous polymer fibers having diametersgenerally larger than diameters of fibers of the lower zone andgenerally smaller than diameters of fibers of the upper zone.
 46. Thefiber structure of claim 44 in which a ratio of an amount of fiberstructure strengthening element to an amount of all the fibers of a zoneof layers is higher in the lower zone than in the upper zone.
 47. Thefiber structure of claim 39 wherein the fiber structural strengtheningelement is made from a different polymer than the fibers of theplurality of layers.
 48. The fiber structure of claim 47 in which thefiber structural strengthening element comprises an adsorbent material.49. The fiber structure of claim 47 in which the fiber structuralstrengthening element comprises an absorbent material.
 50. The fiberstructure of claim 39 in which the fiber structural strengtheningelement comprises a catalyst.
 51. The fiber structure of claim 39 inwhich the structure is cylindrical and comprises a plurality ofconcentric zones, each zone having a different density than eachadjacent zone.
 52. The fiber structure of claim 51 in which thecylindrical structure comprises: a core zone of essentially continuouspolymer filaments; an intermediate zone of essentially continuouspolymer filaments surrounding the core zone, the intermediate zone beinggenerally less dense than the core zone; and an outer zone ofessentially continuous polymer filaments surrounding the intermediatezone, the outer zone being generally less dense than the intermediatezone.
 53. The fiber structure of claim 39 in which the fiber structuralstrengthening element bonds the plurality of the layers together. 54.The fiber structure of claim 39 in which the fiber structuralstrengthening element interlocks the plurality of the layers.
 55. Thefiber structure of claim 39 in which the fiber structural strengtheningelement crystallizes the fibers of the plurality of the layers.